Liquid crystal displays have been used in various electronic devices. A Vertically Aligned Mode (VA mode) liquid crystal display is developed to provide a wider viewing range. In the VA mode, when a user looks at this LCD from the oblique direction, the skin color of Asian people (light orange or pink) appears bluish or whitish. Such a phenomenon is called color wash-out.
The transmittance-voltage (T-V) characteristic of the VA mode liquid crystal display is shown in FIG. 1A and FIG. 1B. The vertical axis is the transmittance rate. The horizontal axis is the applied voltage. When the applied voltage is increased, the transmittance rate curve 102 in the normal direction is also increased. The transmittance changes monotonically as the applied voltage increases. However, in the oblique direction, the transmittance rate curve 104 winds and the various gray scales become the same. This is the main reason to cause the color wash-out.
A method, called Half-tone technology developed by H. Yoshida et al. (Fujitsu Display Technologies Corporation), is provided to improve the foregoing problem. This method combines two different T-V characteristics in one pixel. FIG. 1B illustrates the Half-tone technology. The line 106 in FIG. 1B shows the T-V characteristics with a lower threshold voltage. The line 108 in FIG. 1B shows the T-V characteristics with a higher threshold voltage. By optimizing the threshold voltage and combining transmittance of these two lines, monotonic characteristics can be realized, as shown by the line 110 in FIG. 1B.
There are two types of Half-tone technologies, CC type and TT type. FIG. 2A illustrates the CC type Half-Tone technology. FIG. 2B illustrates the TT type Half-tone technology. According to the two types of Half-tone technologies, a pixel unit is divided into two sub pixels, the first sub-pixel and the second sub-pixel. Different Gamma curves are generated by the first sub-pixel and the second sub-pixel respectively. There, the color shift phenomenon is removed by mixing the two Gamma curves. FIG. 2C illustrates the Gamma curve of a CC type and FIG. 2D illustrates the Gamma curve of a TT type. For example, in FIG. 2C, according to a special applied voltage, the Gamma curve of the first sub-pixel and the Gamma curve of the second sub-pixel are mixed to form the Gamma curve of the pixel unit.
In FIG. 2A, a pixel unit is divided into two regions. A voltage divider composed of two capacitors 214 and 210 is used to form two Gamma curves of two sub-pixel electrodes 206 and 212 respectively. A data voltage in the data line is transferred to the sub-pixel electrode 206 through the transistor 202 to form the electric potential thereon. On the other hand, the electrical potential of the sub-pixel electrode is determined by the data line through capacitor 210. That is, the sub-pixel electrode 212 is in a floating state. Its electric potential is determined by a coupling effect. Charge is trapped into the sub-pixel electrode 212 to shift the electric potential thereon. That affects the quality of a panel.
In FIG. 2B, a pixel unit is divided into two regions. Two thin film transistors 218 and 220 and two capacitors are arranged in the two regions respectively. Two scanning lines or two data lines are used to drive transistors 218 and 220 respectively to form two different Gamma curves to improve the display image quality. However, such structure requires two scanning lines or two data lines to drive a pixel unit, which reduces the aperture ratio and complicates the circuit.
Therefore, a pixel unit and liquid crystal display driving method thereof is required to resolve the foregoing problems.